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Cant, Cant Deficiency, Catenery, Check Gauge, Check Rail, Corrugation, Cross Level
Top, Track Gauge, Twist, Truck
3rd RailThe 3rd rail is used to supply power to electric locomotives. The circuit is completed using the running rails or a 4th rail
A 4th rail is used (rarely) to complete the circuit on electrified lines. See 3rd rail
Term used to describe gap between running rails. See track gauge
Term used to describe distance between up and down lines.
Degree to which the ends of a rail are worn. Wear is usually due to joint movement or voids.
BogieTruck
Rotating undercarriage found at each end of rolling stock. Usually consists of four wheels on two axles.
CantDesired Super-elevation
Cant is the desired and designed inclination of the track and is calculated from track curvature, speed limits, axle weights etc. After a period of use, subsidence may lead to a super-elevation that is deficient in cant, this shortfall is equivalent to cross-level.
Overhead Power
The Catenery is a system of suspended, electrified cables. An electric locomotive receives power from the cable using a pantograph.
Check GaugeThe check gauge is the gap between the check rail and the opposite running rail.
Check RailA check rail is an object placed alongside the running rail to prevent inward movement of the wheel, especially at crossings and on curves.
Corrugation is very short wave undulations in the vertical profile of the rail. Wavelengths are much less than 1m.
Cross LevelThe cross-level is the difference between the actual super-elevation and the desired cant. In both the examples below the right hand rail is low on cross level.
Data-loggingData-logging is the process of capturing information from measurement sensors and saving it into an electronic memory. This data may be retrieved.
FlangewayThe flangeway width is the gap between the check rail and running rail.
Head WearDue to the passage of heavy traffic, the top of a rail will become worn down. The measurement of head wear is given as the reduction in height of the rail from the nominal new rail size.
Dynamic Measurement
The geometry of the track may be different when loaded or unloaded, i.e. when a train is passing. This may be due to voids beneath sleepers or loose chairs.
Possession is the authority to exclusively use a section of track. Depending on local regulations, it is permissible to carry out work or inspection on track without possession provided that all equipment may be removed instantly into a safe area.
Running rails are the pair that support the weight of the rolling stock.
Side WearDue to the centrifugal force of traffic in a curve, the side of a rail will become worn down. The measurement of side wear is given as the reduction in width of the rail from the nominal new rail size. This is measured at a specific point below the rail head (P-point).
StaggerStagger is the perpendicular distance between an overhead conductor wire or supporting cable and the centreline of the track.
Super-elevationSuper-elevation is the measured height difference between the two running rails, whether this height is intentional or otherwise.
The running rail gauge is the distance between the left and right running edge. The gap is measured at a specific point below the rail head (P-point).
Measurement of track gauge is useful in identifying deterioration in the track due to rail side wear or chair movement.
The measurement may depend on whether the track is in a loaded or unloaded condition.
TwistTwist is the rate of change of super-elevation. A degree of twist must occur during the transition between tangential and curved track. Twist becomes a danger if it exceeds the suspension travel in a bogie, i.e. a wheel will lift free. Hence twist is usually measured over the wheelbase of the most common rolling stock bogie.
Top, Vertical Curvature
Vertical alignment is the degree to which the track undulates in the vertical plane. Vertical alignment must be measured to predict interaction and possible resonance with rolling stock at certain speeds and with characteristic suspension/damping properties.
Wavelengths greater than 200m may be ignored as being natural hills and valleys. Wavelengths under 1m are normally called corrugation. Wavelengths that pose particular problems are:
Warp, not to be confused with twist, is the greatest difference in super-elevation anywhere within a given length. It is usually measured over the rolling stock wheelbase or centres of bogies.
WebThe web is the middle part of the rail. As it remains unworn during the life of the rail, the web is a useful reference point. Faults or fracture in the rail web metal may become apparent in time as the web bulges.
